The invention relates to a system for determining the angular spin position of an object spinning about an axis. The object often concerns a projectile the course of which is to be corrected to hit a certain target.
Such systems are known from Netherlands Patent Application No. NL-A 8600710 and Netherlands Patent Appliction No. NL-A 8801203. In these systems at least one polarised carrier wave is transmitted by an antenna unit together with a transmitter unit linked to the antenna unit. The object is fitted with a directional receiving antenna means and a receiving system linked to the receiving antenna means. The system is arranged in such a way that the angular spin position of the object with respect to the antenna unit is measured. The orientation of the antenna unit therefore functions as a reference. For this purpose care is taken that the polarised carrier wave is present around the object. For illumination of the object, a pencil beam is often used. If one polarised carrier wave is transmitted, the angular spin position of the object can be determined with an uncertainty of 180.degree.. Several methods are known to eliminate the 180.degree. uncertainty. A few of these methods are discussed in the said Dutch patent applications. The present invention however also finds application in a system where the angular spin position of the object is determined with a 180.degree. uncertainty.
Because the angular spin position of the object with respect to the antenna unit is measured, for the determination of the angular spin position of the object with respect to space it is also necessary to determine the orientation of the antenna unit with respect to space (the earth surface) and to keep it constant.
Said systems have the disadvantage that determination of the angular spin position of the object with respect to space is calculated on the basis of two measurements: the measurement of the angular spin position of the object with respect to the antenna unit and the measurement of the orientation of the antenna unit with respect to space. Because for the calculation of the angular spin position use is made of two measurements, the accuracy of the calculation will decrease.
Moreover, the software required for the calculation of the angular spin position of the object with respect to space is complicated and thus expensive.
If the antenna unit is placed on a ship, a stabilised platform is to be used onto which the antenna unit is fitted to keep the orientation of the antenna unit with respect to space (see surface) constant when the ship moves.